The invention relates to a cardiac monitor for monitoring the pulsatile flow of blood through the vascular network under the skin of a person and more particularly to a cardiac monitor which monitors reflected light modulated by the pulsatile flow of blood.
The characteristics of individual heartbeats within a single cardiac cycle and the rate of the individual heartbeats have long been recognized as significant indicators of over-all physiological status of the person. The most rudimentary monitoring methods required that the physician sense the cardiac rhythm by acoustic methods or by physically contacting the skin to feel the pulses. The physician was then required to note the differences between the activity he heard or felt and "normal" activity. Information on the rate of heartbeats was only attainable by actually counting the number of cardiac cycles occurring within a predetermined period of time.
Recent advances in electrocardiography have allowed the cardiac activity to be monitored as tiny fluctuations in the electrical potentials between various parts of the body. A drawback of this method is that the small magnitude of these potentials, the presence of muscular artifacts, the requirement for intimate electrical contact as well as the danger of an electrical shock to the person makes this method relatively expensive, cumbersome and of limited utility. Other methods have been attempted including ultrasonic and magnetic equipment, but these methods are seldom used due to their complexity.
The need has developed for a cardiac monitor which may be operated by the individual being monitored such as surviving heart attack victims, potential heart attack victims or physicians themselves. Another need exists for individuals wishing to optimize their physical activities by maintaining an optimum rate of cardiac activity during exercise.
One solution suggested to overcome the problems of the prior art is the use of optical sensing of the biological functions; however, these prior art optical sensing systems also have not provided a convenient, economical and lightweight unit which conveniently allows the individual to obtain rate information normally obtainable from E.C.G. equipment. Furthermore, these systems do not provide a fast and non-complex method of obtaining the heartbeat rate.